1. Field of the Invention
The invention relates to an X-ray tube, comprising an anode and a cathode which are arranged in an evacuated metal envelope comprising a radiation exit window and which carry a positive and a negative high voltage, respectively, with respect to the envelope during operation.
2. Description of the Prior art
An X-ray tube of this kind known from DE-PS 24 55 974 which corresponds to U.S. Pat. No. 4,024,424.
FIG. 1 shows a rotary-anode X-ray tube of this kind in a partly cut open representation. The X-ray tube comprises an evacuated tube envelope 1 which is made of metal and which is referred to hereinafter as a metal envelope, which envelope contains a disc-shaped rotary anode 2 and a cathode 3. The anode 2 and the cathode 3 are journalled and secured, respectively, in the metal envelope in a manner not shown. Journalling is realized via an insulator which is not shown. In the operating condition the anode and the cathode carry a positive and a negative high-voltage potential, respectively, with respect to the metal envelope 1 which carries ground potential.
The X-rays generated at the area of the rotary anode which faces the cathode 3 emerge through a radiation exit window 4 provided in the metal envelope 1. Radiation exit windows of this kind are comparatively thin and are preferably made of beryllium which only slightly attenuates the X-rays. Comparatively strong heating of this window occurs during operation of the X-ray tube.